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Theoretical virtues and theorizing in physics: against the instrumentalist view of simplicity


I argue that if (a) simplicity is a theoretical virtue and (b) some theoretical virtues are the constituents of the aims of theorizing in physics—i.e., theory choice and theory development in physics—and (c) scientific rationality is instrumental rationality, then simplicity cannot be a mere means to achieve the aims. I do this by showing that considering simplicity as a mere means brings about counterintuitive ramifications concerning scientific rationality. These counterintuitive ramifications can be avoided if we consider simplicity a constituent of the aims of theorizing in physics.

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  1. Different catalogs of theoretical virtues can be found in the works of scientists and philosophers of science at least since Robert Boyle’s “Notes on a Good and an Excellent Hypothesis” (1991, p. 119). Most of these catalogs have considerable overlaps. For some examples, see Hempel (1966, 1983), Quine and Ullian (1978), Kuhn (1977), Newton-Smith (1981), McMullin (1996, 2008), Lacey (1999), Lycan (1985), Douglas (2013), and Keas (2018).

  2. In a response to this paper, Kuhn (1983, p. 565) admits that Hempel’s articulation of the aims of science in terms of theoretical virtues is an “improvement” over his own “puzzle-solving” account of the aim of science. Probably the most detailed account of the aims of science in terms of theoretical virtues can be found in Laudan (1984).

  3. For instance, simplicity is mentioned as a theoretical virtue in all the resources that are cited in footnote 1.

  4. Such approach, though not particularly about theoretical physics, is adopted by Kuhn (1977), McMullin (1982), Laudan (1984), and Longino (1990, Chapter 4).

  5. As Kuhn (1977) argues, this does not mean that different members of the community cannot have legitimate disagreements about the interpretation of theoretical virtues or their relative weight in theory choice.

  6. For a non-instrumental account of scientific rationality, see Friedman (2001, pp. 53–68).

  7. Here, a distinction can be made between “subjective rationality” (or rationality vis-à-vis a scientist’s beliefs) and “objective rationality” (or rationality vis-à-vis available evidence). A scientist’s theory choice, for instance, might be subjectively rational because she believes that the chosen theory best instantiates the aim-TVs, but objectively irrational because her relevant beliefs are false—i.e., inconsistent with the evidence. In this paper, I avoid the problem of possible conflicts between objective vs. subjective rationality by assuming that scientists’ relevant beliefs are always justified, namely, their beliefs are supported with the relevant facts of the matter. So, for instance, if scientists believe that T1 is more accurate (or less explanatory powerful) that T2, they are justified in their belief because their belief accord with the evidence. This, of course, does not mean that their beliefs are always true.

  8. As Rowbottom (2010, pp. 212–13) suggests, the achievability of the aims by following the norms or using the means can be also understood probabilistically: it is rational to adopt some means if it makes it more probable to achieve the aims. As we shall see, my arguments can also address probabilistic instrumentality. For the sake of brevity, in what follows, I primarily talk about “achieving the aims” rather than “making achieving the aims more probable.”.


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I am grateful to Anjan Chakravertty, Janet Kourany, Faeze Fazeli, Oliver Traldi, and two anonymous referees for their helpful comments and suggestions.

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Mohammadian, M. Theoretical virtues and theorizing in physics: against the instrumentalist view of simplicity. Synthese 199, 4819–4828 (2021).

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  • Simplicity
  • Theoretical virtues
  • The aims of science
  • Scientific rationality
  • Instrumental rationality